High-harmonic generation from an atomically thin semiconductor

High-harmonic generation (HHG) in bulk solids permits the exploration of materials in a new regime of strong fields and attosecond timescales(1-6). The generation process has been discussed in the context of strongly driven electron dynamics in single-particle bands(7-14). Two-dimensional materials exhibit distinctive electronic properties compared to the bulk that could significantly modify the HHG process(15,16), including different symmetries(17-19), access to individual valleys(20,21) and enhanced many-body interactions(22-25). Here we demonstrate non-perturbative HHG from a monolayer MoS2 crystal, with even and odd harmonics extending to the 13th order. The even orders are predominantly polarized perpendicular to the pump and are compatible with the anomalous transverse intraband current arising from the material's Berry curvature, while the weak parallel component suggests the importance of interband transitions. The odd harmonics exhibit a significant enhancement in effciency per layer compared to the bulk, which is attributed to correlation effects. The combination of strong many-body Coulomb interactions and widely tunable electronic properties in two-dimensionalmaterialsoffers a new platform for attosecond physics.